Method to achieve low and stable ferromagnetic coupling field

ABSTRACT

A method for making spin valves with low and stable coupling field includes the oxygen exposure steps. In this method, a first ferromagnetic layer is deposited onto a substrate using an ion beam sputtering process. The first surface of the first ferromagnetic layer is exposed to an oxygen-rich atmosphere with oxygen partial pressure of about 5×10 −6  Torr. Oxygen is physisorbed on the first surface. The oxygen partial pressure rapidly decreases to below 10 −8  Torr levels before a spacer layer of about 20 Å thick copper is deposited onto the first oxygen treated surface. The spacer layer has a second surface, which is treated with oxygen with a process similar to the process for treating the first surface. The oxygen partial pressure rapidly decreases to below 10 −8  Torr levels before a second ferromagnetic layer is deposited onto the second oxygen treated surface. Surface adsorption of oxygen limits the intermixing between the layers and reduces the surface roughness of these surfaces, which results in reducing the coupling field of the spin valves. The coupling field is extremely stable upon hard bake anneal. The magnetoresistive ratio also is significantly enhanced. This method can be applied for top and bottom simple spin valves, top and bottom AP-pinned spin valves, and dual spin valves.

[0001] This application is a divisional of application Ser. No.09/618,167, filed on Jul. 17, 2000.

FIELD OF THE INVENTION

[0002] This invention relates generally to spin valves. Moreparticularly, it relates to the coupling field of spin valves.

BACKGROUND ART

[0003] A spin valve or a magnetoresistive (MR) sensor detects magneticfield signals through the resistance changes of a read element,fabricated of a magnetic material, as a function of the strength anddirection of magnetic flux being sensed by the read element. Theconventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which a component of the read elementresistance varies as the square of the cosine of the angle between themagnetization in the read element and the direction of sense currentflow through the read element. Such a MR Sensor can be used to read datafrom a magnetic medium. An external magnetic field from the magneticmedium (the signal field) causes a change in the direction ofmagnetization in the read element, which in turn causes a change inresistance (ΔR/R) in the read element and a corresponding change in thesensed current or voltage.

[0004] A spin valve has been identified in which the resistance betweentwo uncoupled ferromagnetic layers varies as the cosine of the anglebetween the magnetizations of the two layers and is independent of thedirection of current flow.

[0005] An external magnetic field causes a variation in the relativeorientation of the magnetization of neighboring ferromagnetic layers ina spin valve. This in turn causes a change in the spin-dependentscattering of conduction electrons and thus the electrical resistance ofthe spin valve. The resistance of the spin valve thus changes as therelative alignment of the magnetizations of the ferromagnetic layerschanges.

[0006] Typically, a conventional simple spin valve comprises aferromagnetic free layer, a spacer layer, and a single-layer pinnedferromagnetic layer, which is exchange-coupled with ananti-ferromagnetic (AF) layer. In an anti-parallel (AP) pinned spinvalve, the single-layer pinned ferromagnetic layer is replaced by alaminated structure comprising at least two ferromagnetic pinnedsublayers separated by one or more thin non-ferromagnetic anti-couplingsublayers.

[0007] In general, the larger the value of ΔR/R and the smaller thecoupling field H_(f), the better the performance of the spin value. TheΔR/R value of a spin valve conventionally increases as the thickness ofthe spacer layer decreases due to the reduced shunting of the sensecurrent in the spacer layer of the spin valve. For example, a spin valvewith a copper spacer layer having a thickness of 28 Å will achieve aΔR/R of about 5%. If the thickness of copper spacer is reduced to 20 Å,a ΔR/R of 8% will be obtained. However, the ferromagnetic coupling fieldH_(f) also increases as the thickness of the spacer layer decreases. Inaddition, the ferromagnetic coupling field of conventional spin valvesis unstable upon annealing cycles. For example, the ferromagneticcoupling field of spin valves changes from about +5 Oe at the beginningof the annealing process to +20 Oe after annealing cycles.

[0008] An article entitled “Oxygen as a Surfactant in the Growth ofGiant Magnetoresistance Spin Valve” published Dec. 15, 1997 by Journalof Applied Physic to Egelhoff et al. discloses a method for increasingthe giant magnetoresistance of ΔR/R of Co/Cu spin valves with use ofoxygen. In this method, oxygen is introduced in an ultrahigh vacuumdeposition chamber with an oxygen partial pressure of 5×10⁻⁹ Torr duringdeposition of the spin valve layers, or the top copper surface isexposed to the oxygen to achieve an oxygen coverage, after which growthof the sample is completed. The oxygen acts as a surfactant during filmgrowth to suppress defects and to create a surface that scatterselectrons more specularly. Oxygen coverage decreases the ferromagneticcoupling between magnetic layers, and decreases the sheet resistance ofspin valves.

[0009] Unfortunately, this technique requires a very small oxygenpartial pressure window around 5×10⁻⁹ Torr, since when the oxygenpartial pressure is increased to only 10⁻⁸ Torr, all GMR (ΔR/R) gain dueto oxygen is lost, and at oxygen pressures higher than this, thefall-off in GMR is rapid. This very small oxygen partial pressure isvery difficult to achieve or to maintain in a large manufacturing typesystem. Also, oxygen exposure of only one surface of the copper spacerlayer does not optimize the ferromagnetic coupling field. Furthermore,the use of oxygen for all spin valve layer depositions may result inoxidation of Mn in anti-ferromagnetic materials, such as FeMn, PtMn,IrMn, PdPtMn and NiMn, and thus kills the spin valve effect. Thereforethis technique can not be applied for spin valve deposition.

[0010] In addition, adsorbing oxygen only on the copper surface does notimprove the GMR, and produces only a positive coupling field.Furthermore, this technique results in a decrease in sheet resistance,which reduces the overall signal. Finally, prior art oxygen treatmentdoes not show stabilization of the ferromagnetic coupling field uponhard bake annealing cycles.

[0011] There is a need, therefore, for an improved method of making spinvalves that overcomes the above difficulties.

OBJECTS AND ADVANTAGES

[0012] Accordingly, it is a primary object of the present invention toprovide spin valves with low and stable coupling field H_(f).

[0013] It is a further object of the invention to provide spin valveswith high magnetoresistive ratio ΔR/R.

[0014] It is another object of the invention to develop a process ofmaking spin valves with oxygen partial pressure levels can be used inmanufacturing systems.

[0015] It is another object of the invention to develop a process ofmaking spin valves achieving negative coupling fields in productionprocesses.

[0016] It is a further object of the invention to develop a process ofmaking spin valves, which does not result in reduction in sheetresistance.

[0017] It is another object of the invention to develop a process ofmaking spin valves, which can be used with metallic anti-ferromagneticmaterials or oxide in addition to oxide antiferromagnetic materials.

[0018] It is an additional object of the invention to provide a methodof making spin valves having the above properties, which can be appliedfor bottom and top spin valves.

SUMMARY

[0019] These objects and advantages are attained by spin valves having afirst surface of one ferromagnetic layer and a second surface of aspacer layer, treated with oxygen.

[0020] According to a first embodiment of the present invention, asimple spin valve includes a ferromagnetic layer having a first surface,such as a ferromagnetic free layer, and a spacer layer having a secondsurface. One or more of the first and second surfaces has been treatedwith oxygen after deposition of the corresponding layers and oxygentreatment has been shut off before depositing a subsequent layer.Treatment with oxygen herein refers to exposing a surface of a layer ofmaterial to oxygen after the layer has been deposited. Physisorbedoxygen on these surfaces limits the intermixing between the layers andreduces the surface roughness of the surfaces. As a result, the couplingfield is reduced. The obtained coupling field is around −10 Oe for about20 Å copper, and the coupling field is stable upon hard bake annealingcycles at 232° C. for 11 hours or at 270° C. for 6 hours. Furthermore,the magnetoresistive ratio ΔR/R is enhanced from about 6% to about 9%.

[0021] According to a second embodiment of the present invention, abottom AP-pinned spin valve includes a first surface of a ferromagneticlayer, which is an AP-pinned sublayer, and a second surface of a spacerlayer, treated with oxygen. The effect of oxygen surface treatment inAP-pinned spin valves is similar to the effect of oxygen surfacetreatment in simple spin valve as described in the first embodiment.

[0022] A method of making spin valves having surfaces treated withoxygen is described in a third embodiment of the present invention. Anion beam sputtering technique may be used to make the spin valves. Asubstrate is provided in a vacuum chamber. A first ferromagnetic layer,which may be a free layer for a top spin valve or a pinned layer for abottom spin valve, is deposited onto the substrate. A first surface ofthe first ferromagnetic layer is exposed to an oxygen-rich atmospherewith oxygen partial pressure of between about 1×10⁻⁷ Torr and about5×10⁻⁵ Torr, by introducing an oxygen burst into the vacuum chamber forabout 30 seconds. The oxygen molecules are directed toward thesubstrate, and a substrate shutter is fully open to directly expose theoxygen beam. Oxygen is physisorbed on the first surface. After about 30seconds, the oxygen is shut off, and the normal process of fabricationof the spin valve is resumed. A spacer layer of about 20 Å thick isdeposited on the oxygen treated surface. A second oxygen burst isintroduced into the vacuum chamber with an oxygen partial pressure ofabout 5×10⁻⁶ Torr for treating a second surface of the spacer layer. Theprocess of treating this second surface is similar to the process oftreating the first surface as described above. The oxygen is again shutoff before a second ferromagnetic layer, which may be a pinned layer fora top spin valve or a free layer bottom spin valve, is subsequentlydeposited.

[0023] The method described in the third embodiment may be used for topand bottom simple spin valves, top and bottom AP-pinned spin valves, anddual spin valves.

[0024] According to a third embodiment of the present invention, spinvalves of the types depicted in the first and second embodiments, whichare made by the method described in the third embodiment, areincorporated in a GMR read/write head. The GMR read/write head includesa lower shield layer and an upper shield layer, which sandwich a spinvalve, a lower gap disposed between the lower shield and the spin valve,and an upper gap disposed between the upper shield and the spin valve.The spin valve converts a magnetic signal to an electrical signal byusing the magnetoresistive effect generated by a relative angle betweenmagnetizing directions of a ferromagnetic free layer and a ferromagneticpinned layer.

[0025] A GMR read/write head of the type depicted in the fourthembodiment is incorporated in a disk drive system including a magneticrecording disk, a motor for spinning the magnetic recording disk, theread/write head and an actuator for moving the read/write head acrossthe magnetic recording disk, according to a fifth embodiment of thepresent invention.

BRIEF DESCRIPTION OF THE FIGURES

[0026]FIG. 1 is a cross-sectional schematic diagram of a top simple spinvalve according to a first embodiment of the present invention;

[0027]FIG. 2 is a cross-sectional schematic diagram of a bottomAP-pinned spin valve according to a second embodiment of the presentinvention;

[0028] FIGS. 3A-F are cross-sectional schematic diagrams illustratingthe steps of a process making spin valves with low and stable couplingfield according to a third embodiment of the present invention;

[0029]FIG. 4 is a graph illustrating a plot of roughness as a functionof oxygen flow with copper spacer thickness of 20 Å for an AP-pinnedspin valve;

[0030]FIG. 5 is a graph illustrating a plot of sheet resistance as afunction of oxygen flow with the copper spacer layer thickness of 20 Åfor an AP-pinned spin valve;

[0031]FIG. 6 is a graph illustrating a plot of magnetoresistive ratioΔR/R as a function of oxygen flow with the copper spacer layer thicknessof 20 Å for an AP-pinned spin valve;

[0032]FIG. 7 is a graph illustrating a plot of coupling field as afunction of oxygen flow with the copper spacer layer thickness of 20 Åfor an AP-pinned spin valve;

[0033]FIG. 8 is a graph illustrating a plot of coercive field as afunction of oxygen flow with the copper spacer layer thickness of 20 Åfor an AP-pinned spin valve;

[0034]FIG. 9 is a graph depicting plots illustrating the properties ofAP-pinned spin valves as functions of copper spacer layer depositiontime with a constant oxygen flow of 2 sccm;

[0035]FIG. 10 is a graph depicting only two plots of magnetoresistiveratio (ΔR/R) and coupling field H_(f) as functions of copper spacerlayer deposition time illustrated in FIG. 9;

[0036]FIG. 11 is a schematic diagram of a GMR read/write head accordingto a fourth embodiment of the present invention; and

[0037]FIG. 12 is a schematic diagram of a disk drive system according toa fifth embodiment of the present invention.

DETAILED DESCRIPTION

[0038] Although the following detailed description contains manyspecifics for the purposes of illustration, anyone of ordinary skill inthe art will appreciate that many variations and alterations to thefollowing details are within the scope of the invention. Accordingly,the following preferred embodiment of the invention is set forth withoutany loss of generality to, and without imposing limitations upon, theclaimed invention.

[0039]FIG. 1 is a cross-sectional schematic diagram illustrating a layerstructure of a top simple spin valve 100 according to a first embodimentof the present invention. The spin valve 100 includes a ferromagneticfree layer 105 including a ferromagnetic layer 106 contacting ananolayer 108 having a first surface 109, a ferromagnetic pinned layer112, and a spacer layer 110, which has a second surface 111, disposedbetween the ferromagnetic free layer 105 and the ferromagnetic pinnedlayer 112. The spin valve 100 may further include an anti-ferromagnetic(AF) layer 114, disposed between the ferromagnetic pinned layer 112 anda cap layer 116, and a oxide seed layer 104 proximate the ferromagneticfree layer 105. The nanolayer 108 enhances the magnetoresistive ratio(ΔR/R) for the spin valve 100.

[0040] Ferromagnetic layer 106 typically includes a material containingNi, Fe, Co or alloys of Ni, Fe and Co such as NiFe, NiCo, and FeCo. Theferromagnetic pinned layer 112 is typically made of Co or CoFe. Thespacer layer 110 is typically made of Cu, Ag, Au or their alloys. The AFlayer 114 typically includes a material containing Mn, such as FeMn,PtMn, IrMn, PdPtMn and NiMn. The nanolayer 108 is typically made ofCoFe, and the cap layer 116 typically includes Ta. Oxide seed layer 104is typically made of NiMnO.

[0041] The first surface 109 and the second surface 111 are treated withoxygen during an ion beam sputtering process of making the spin valve100. The oxygen treatment of the surface 109 or 111 occurs after thedeposition of the corresponding layer 108 or 110. The first surface 109may be exposed to oxygen after nanolayer 108 has been deposited.Similarily the second surface 111 may be exposed to oxygen after thespacer layer 110 has been deposited. Oxygen exposure may be restrictedduring the deposition of nanolayer 108 and spacer layer 110. Oxygentreated surfaces 109 and 111 limit the intermixing between the nanolayer108 and the spacer layer 110, and between the spacer layer 110 and thepinned layer 112 respectively. By treating the surface with oxygen afterdeposition of the corresponding layers, higher oxygen partial pressuresmay be used compared to the oxygen partial pressures previously usedwhen treating layers with oxygen during deposition. Consequently, spinvalves such as spin valve 100 may be fabricated with existingmanufacturing type deposition equipment. Furthermore, if oxygen exposureis restricted after deposition, oxygen sensitive layers, such as Mncontaining layers, will not be undesirably exposed to the risk ofoxidation.

[0042] These oxygen treated surfaces 109 and 111 reduce the surfaceroughness, therefore the ferromagnetic coupling H_(f) of the spin valve100 is reduced. The obtained coupling field H_(f) of spin valve 100 isbetween about −10 Oe and about +10 Oe, which is stable upon the hardbake annealing cycles at 232° C. for 11 hours, or at 270° C. for 6hours. In addition, the magnetoresistive ratio ΔR/R of spin valve 100 isalso enhanced from about 6% to about 9%.

[0043]FIG. 2 is a cross sectional schematic diagram illustrating a layerstructure of a bottom AP-pinned spin valve 200 according to a secondembodiment of the present invention. The AP-pinned spin valve 200includes a ferromagnetic free layer 205 including a ferromagnetic layer206 contacting a nanolayer 208, an AP ferromagnetic pinned layer 212,and a spacer layer 210 located between the ferromagnetic free layer 205and the AP-pinned layer 212. The AP-pinned spin valve 200 furtherincludes an AF layer 214 disposed between the AP-pinned layer 212 and ametal seed layer 216, two oxide seed layer 202 and 204 under the metalseed layer 216, and a cap layer 218 disposed on top of the ferromagneticfree layer 206. The material of each layer of AP-pinned spin valve 200,except the AP-pinned layer 212 and the oxide seed layer 202, is similarto those of the corresponding layers of the simple spin valve 100 asdescribed in FIG. 1. The oxide seed layer 202 is typically made ofAl₂O₃.

[0044] The AP-pinned layer 212 includes a first ferromagnetic pinnedsublayer 220, a second ferromagnetic pinned sublayer 224, and ananti-parallel (AP) pinned spacer sublayer 222 between the first pinnedsublayer 220 and the second pinned sublayer 224. Two ferromagneticpinned sublayers 220 and 224 are typically made of CoFe, the AP pinnedspacer sublayer 222 is typically made of Ru, Cr, Rh or Cu, or theiralloys.

[0045] The second ferromagnetic pinned sublayer 224 includes a firstsurface 211, and the spacer layer 210 has a second surface 209. In thisembodiment the first surface 211 corresponds to ferromagnetic pinnedsublayer 224 and the second surface 209 corresponds to the spacer layer210. The first and the second surfaces 211 and 209 are treated withoxygen after depositing corresponding layers 224 and 210. The oxygentreatment generally takes place during the fabrication of the AP-pinnedspin valve 200. The effect of oxygen treated surfaces 209 and 211 on theroughness and the coupling field H_(f) of AP-pinned spin valve 200 issimilar to the effect of oxygen treated surfaces 109 and 111 of simplespin valve 100 as described in FIG. 1. The coupling field H_(f) ofAP-pinned spin valve 200 is around −10 Oe, and the magnetoresistiveratio ΔR/R of AP-pinned spin valve 200 is enhanced from about 5.5% and7.7%.

[0046] An ion beam sputtering method may be used to produce spin valvesof the types depicted in FIGS. 1 and 2 to easily control the depositionbetween wafers or within a wafer. An exemplary sputtering method isdisclosed in U.S. Pat. No. 5,871,622 issued Feb. 16, 1999 and U.S. Pat.No. 5,492,605 issued Feb. 20, 1996 by the inventor. FIGS. 3A-F arecross-sectional schematic diagrams illustrating the steps of making spinvalves of the types depicted in FIGS. 1 and 2. As shown in FIG. 3A, afirst ferromagnetic layer 304 is deposited on a substrate 302 in avacuum chamber. First ferromagnetic layer 304 may be a free layer for atop spin valve or a pinned layer for a bottom spin valve. A first oxygenburst is introduced in to the vacuum chamber with oxygen partialpressure of about 5×10⁻⁶ Torr. A first surface 305 of the firstferromagnetic layer 304 is exposed to this oxygen-rich atmosphere.Oxygen molecules are directed toward the substrate 302 and the substrateshutter, which is not shown in FIG. 3A, is fully open to directly exposefirst surface 305 to the oxygen. As a result, oxygen is physisorbed onthe first surface 305 to produce a first oxgen treated surface 306.

[0047] An oxygen valve controlling the flow of oxygen to the chamber isthen shut to reduce the oxygen partial pressure. After the oxygen valveis shut, the deposition process resumes. A spacer layer 308 is depositedon the first oxygen treated surface 306 which is shown in FIG. 3B. Thespacer layer 308 is deposited over the oxygen treated surface 306 forapproximately 30 seconds and has a thickness of about 20 Å. The spacerlayer 308 has a second surface 309 that is treated with oxygen using amethod similar to the method of treating the first surface 305 withoxygen as described in FIG. 3A. As shown in FIG. 3C, the second surface309 is exposed in an oxygen partial pressure of about 5×10⁻⁶ Torr, andoxygen is physisorbed on the second surface 309 to produce a secondoxygen treated surface 310. Note that the oxygen treatment of surfaces305 and 309 take place after the deposition of the corresponding layers304 and 308. After the oxygen valve is shut off again a secondferromagnetic layer 312, e.g., a ferromagnetic pinned layer for a topspin valve or a ferromagnetic free layer for a bottom spin valve, issubsequently deposited onto the second oxygen treated surface 310 asshown in FIG. 3D.

[0048] The process of making the spin valve 300 as described in FIGS.3A-D does not require any additional steps to incorporate the oxygenburst into the standard spin valve of the prior art. This process may beused for top and bottom simple spin valves, top and bottom AP-pinnedspin valves, and dual spin valves.

[0049] Experimental Results

[0050] An example is given below to show the oxygen exposure ofdifferent surfaces and how it affects the coupling field H_(f) of simpletop spin valves. A simple spin valve generally includes an oxide seedlayer of NiMnO 30 Å thick, a free layer including a ferromagnetic layerof NiFe 45 Å thick and a nanolayer of CoFe 15 Å thick, a spacer layer ofCu 20 Å thick, a pinned layer of CoFe 24 Å thick, an AF layer of IrMn 80Å thick, and a cap layer of Ta 50 Å thick. Table 1 below shows theproperties of two simple spin valves A and B, which have the samestructure as described, except for the oxygen exposed surfaces. In spinvalve A only the surface of Cu spacer layer, corresponding to layer 111of FIG. 1, has been exposed to oxygen as described above. In spin valveB, the surfaces of the CoFe layer and Cu spacer layer, corresponding tosurfaces 109 and 111 in FIG. 1, have been treated with oxygen. TABLE 1Spin valve A Spin valve B ΔR/R (%) 8.32 8.35 R (Ohms/sq) 20 20 H_(f)(Oe) 16 6.5 H_(c) (Oe) 4 5

[0051] The data in the Table 1 shows that the coupling field H_(f) isabout 2.5 times smaller when the spin valve has oxygen exposure of bothCu and CoFe surfaces compared to when the spin valve has oxygen exposureof the Cu surface only. The coupling field H_(f) of simple spin valve Bdoes not degrade upon hard bake annealing at 232° C. Indeed the spinvalve B, which was annealed at 232° C. for 11 hours or at 270° C. for 6hours, maintained a coupling field at around 8 Oe.

[0052] The effect of oxygen surface treatment as described in FIGS. 2-3on the properties of bottom AP-pinned PtMn spin valves is shown in FIGS.4-9. A bottom AP pinned PtMn spin valve generally includes a first oxideseed layer of Al₂O₃ 30 Å thick, a second oxide seed layer of NiMnO 30 Åthick, a metal seed layer of Ta 35 Å thick, an AF layer of PtMn 250 Åthick, a first pinned sublayer of CoFe 17 Å thick, an AP pinned spacersublayer of Ru 8 Å thick, a second pinned sublayer of CoFe 26 Å thick, aspacer layer of Cu 20 Å thick, a free layer including a ferromagneticlayer of NiFe 45 Å thick and a nanolayer of CoFe 15 Å thick, and a caplayer of Ta 50 Å thick. FIGS. 4-8 are plots of the surface roughness Ra,coupling field H_(f), sheet resistance R, magnetoresistive ratio ΔR/R,and coercive field H_(c) as functions of oxygen flow for an AP-pinnedspin valve of the type depicted in FIG. 2. The spin valve in FIGS. 4-8has a spacer layer about 20 Å thick. As shown in FIG. 4, the surfaceroughness Ra is typically about 2.9 Å when the first and second surfacesare not treated with oxygen. The surface roughness Ra decreases fromabout 2.9 Å to a minimum value of about 1.75 Å as the oxygen flowincreases from zero to about 2 sccm. After this point, the surfaceroughness Ra increases as the oxygen flow increases. Therefore, thesurface roughness is minimized at an oxygen flow of about 2 sccm.(e.g.5×10⁻⁶ Torr oxygen partial pressure)

[0053] As shown in FIG. 5, the sheet resistance of an AP-pinned spinvalve without oxygen surface treatment is typically about 19 Ohms/sq,which does not vary much as the oxygen flow increases. The sheetresistance typically stays constant when the oxygen flow is in a rangeof from about 1.5 sccm to about 3 sccm. The sheet resistance R istypically about 19 Ohms/sq for an oxygen flow of about 2 sccm.

[0054] The improvements of the magnetoresistive ratio ΔR/R and thecoupling field H_(f) of an AP-pinned spin valve are shown in FIGS. 6 and7 respectively. The magnetoresistive ratio ΔR/R is typically about 6%with a coupling field H_(f) of about 56 Oe when the first and secondsurfaces of the AP spin valve are not treated with oxygen. ΔR/Rincreases to about 7.6%, and the coupling field H_(f) decreases rapidlyto about 17 Oe as the oxygen flow is typically about 0.5 sccm. Thecoupling field decreases from about 17 Oe to about −11 Oe, while ΔR/R ofabout 7.6% does not vary as the oxygen flow increases from about 0.5sccm to about 2.5 sccm. After this point, ΔR/R typically decreases andthe coupling field H_(f) typically increases as the oxygen flowincreases. The coupling field H_(f) is about −9 Oe for an oxygen flow ofabout 2 sccm.

[0055] In FIG. 8, the coercive field H_(c) decreases from about 6 Oe toabout 5 Oe as the oxygen flow increases from zero to about 0.5 sccm.After that, the coercive field slowly increases as the oxygen flowincreases. The maximum value of H_(c) is typically about 7 Oe obtainedas an oxygen flow of about 3.5 sccm. The coercive field H_(c) rapidlydrops down to about 2 Oe when the oxygen flow is greater than 3.5 sccm.

[0056]FIG. 9 is a graph illustrating the plots of magnetoresistive ratioΔR/R, sheet resistance R, coupling field H_(f), and coercive field H_(c)as functions of spacer layer deposition time with an oxygen flow ofabout 2 sccm. In this case, the spacer layer is made of copper. As shownin FIG. 9, the coupling field H_(f) rapidly decreases from about 39 Oeto about −5 Oe as the copper deposition time increases from about 25seconds to about 30 seconds. The copper deposition rate is typicallyabout 0.65 Å second. After about 30 seconds the coupling field H_(f)typically increases as the copper deposition time increases. The minimumvalue of H_(f), which is typically about −5 Oe is obtained after copperis deposited for about 30 seconds. The sheet resistance R of about 19Ohms/sq, the magnetoresistive ratio ΔR/R of about 7.6%, and the coercivefield H_(c) of 6 Oe are obtained when the deposition of the copperspacer layer is between about 25 seconds to 34 seconds. FIG. 10 is agraph illustrating the plots of coupling field H_(f) andmagnetoresistive ratio ΔR/R, which are depicted in FIG. 9, for the sakeof clarity.

[0057] Spin valves of the types described above with respect to FIGS. 1,2 and 3D may be incorporated into a GMR read/write head 404 as shown inFIG. 11. The GMR read/write head 404 includes a first shield 403 andsecond shield 409 sandwiching a spin valve 401. The GMR read/write head404 further includes a first gap 405 between the first shield 403 andthe spin valve 401, and a second gap 407 between the second shield 409and the spin valve 401. Spin valve 401 converts a magnetic signal to anelectrical signal by using the magnetoresistive effect generated by arelative angle between magnetization directions of at least twoferromagnetic layers of spin valve 401.

[0058] The GMR read/write head depicted in FIG. 11 may be incorporatedinto a disk drive system 400 as shown in FIG. 12. The disk drive system400 generally comprises a magnetic recording disk 402, a GMR read/writehead 404 containing a spin valve 401, an actuator 406 connected to theread/write head 404, and a motor 408 connected to the disk 402. Themotor 408 spins the disk 402 with respect to read/write head 404. Theactuator 406 moves the read/write head 404 across the magnetic recordingdisk 402 so the read/write head 404 may access different regions ofmagnetically recorded data on the magnetic recording disk 402.

[0059] It will be clear to one skilled in the art that the aboveembodiment may be altered in many ways without departing from the scopeof the invention. Accordingly, the scope of the invention should bedetermined by the following claims and their legal equivalents.

What is claimed is:
 1. A method for making a spin valve comprising: a)providing a substrate; b) depositing a first ferromagnetic layer havinga first surface on the substrate; c ) depositing a spacer layer having asecond surface; d) depositing a second ferromagnetic layer, wherein thespacer layer is disposed between the first and second ferromagneticlayers; and e) exposing one or more of the first and second surfaces toan oxygen partial pressure, then decreasing the oxygen partial pressurebefore depositing a subsequent layer.
 2. The method of claim 1, whereinone or more of the first and second surfaces are exposed to an oxygenpartial pressure of between about 1×10⁻⁷ Torr and about 5×10⁻⁵ Torr. 3.The method of claim 2, wherein the oxygen partial pressure decreasesbelow an oxygen partial pressure level used in exposing the first andsecond surfaces before the depositions of the spacer layer and thesecond ferromagnetic layer.
 4. The method of claim 3, wherein the firstsurface is exposed to the oxygen partial pressure before depositing thespacer layer.
 5. The method of claim 3, wherein the second surface isexposed to the oxygen partial pressure before depositing the secondferromagnetic layer.
 6. The method of claim 1, wherein an ion beamsputtering process is used for depositions of the first ferromagnetic,second ferromagnetic and spacer layers.
 7. The method of claim 1,wherein oxygen molecules are directed toward the substrate, and asubstrate shutter is fully open for the first and second surfaces to bedirectly exposed to the oxygen.